Knowing how to make Half Square Triangles (HSTs) is a useful quilting skill.  These foundational units are used in many blocks, and learning how to make a perfect HST unit will open many design possibilities to your quilting.

There are several methods that quilters have developed to make these classic units. Below are two of the most popular, along with cutting charts for making each type.

Tip

If you want to give yourself some wiggle room, cut your pieces slightly larger than the size given in the chart.  After the unit is completed, trim down to the unfinished* size, making sure the diagonal line of your unit follows a diagonal line on your ruler.

*Don’t accidentally trim off your seam allowance!

Half Square Triangle Unit (Exploded)

Quick Sew Method for making Half Square Triangle (HST) Units

This method creates two HST units at a time, a real time saver!

1. Choose two contrasting fabrics, typically one light and one dark.
2. Cut squares that are 7/8″ larger than your finished size unit. (For example, if your finished HST unit will be 2″, then your squares should be 2 7/8″ square.)
3. On the wrong side of your light square, draw a diagonal line from corner to corner.  Pin the light square to a dark square.
4. Take to your machine and sew 1/4″ to the left of the diagonal line. Turn unit around the other way and sew 1/4″ to the left on the other side of the diagonal line.
5. Cut the unit in half along the drawn diagonal line. 
6. Gently press the seam towards the darker fabric.

Cutting Instructions for Quick Sew Method

Using a Half Square Triangle Ruler

To use this method, you will need a HST ruler, such as the one made by Creative Grids. The advantage of this method, is the quick precise cutting method, and how easily these units can be chain pieced, allowing you to cut and sew the units rather quickly. This is the way to go if you are making LOTS of HSTs.

1. Determine the finished size you need your unit to be.
2. Cut strips from two contrasting fabrics the width of your finished size unit.  For example, for 2″ HST units, you should cut your strips 2″ wide.
3. Place two contrasting strips right sides together (RST), making sure the raw edges along the long sides of the strips are perfectly aligned. It is helpful to place a pin in one end of the set to minimize shifting.
4. If you are right handed, square off the left end of the strip set. Align your ruler so that the bottom of the strip set lines up with the marked line for the width of your strip, and so that the left edge of the ruler lines up with the squared off edge of the set. In our example of 2″ HST finished units, you would align the bottom of the strip with the 2″ line. (If you are left handed, you should reverse these instructions.)
5. Cut your strip along the diagonal of the ruler. Place a pin in the two fabrics you just cut.
6. Turn the ruler 180 degrees and this time align the TOP of the strip with the measuring line (Again, in our example this would be the 2″ line.) Pin the cut pieces
7. Continue along the strip until you have cut as many triangular sets as possible.
8. Take the cut sets to your machine and sew along the diagonal using a 1/4″ seam.
9. Gently press to the dark side.